The main objective of the proposed research is to study the molecular events associated with the life-cycle of the human pathogenic parvovirus B19 believed to be the etiologic agent for several human diseases such as erythema infectiosum, transient aplastic crisis associated with several types of hemolytic anemias including sickle cell disease, post-infection anthropathy and possibly hydrops fetalis. In view of the clinical importance of B19, cellular and molecular biology of this parvovirus will be studied as follows: 1. The target cell in the erythroid lineage of human bone marrow cells for the B19 infection will be further characterized by isolating highly enriched hematopoietic progenitor cells by sorting with monoclonal antibodies recognized by human progenitor cells. Production of high-titer B19 progeny virus in this cell culture system will facilitate further studies on the virus-host cell interactions, and the molecular events throughout the course of the viral infection. 2. A generalized transcription map of the B19 viral genome will be constructed by characterizing all the major promoters and the viral RNA transcripts including mapping of the 5' - and 3' -termini and the splice-sites n the RNA transcripts. 3. The structural analysis of the termini of the viral DNA and its replicative intermediates will be carried out to elucidate the underlying mechanism of the viral DNA replication. The possibility of the involvement of a putative protein in the resolution and replication of the viral hairpin DNA termini will also be explored. These studies are aimed at gaining an insight into the molecular basis of the B19 viral pathogenesis in humans. The long-term objectives of these studies are to unravel some of the intricacies of the cellular and molecular interactions of the B19 parvovirus with, and its remarkable specificity for, the hematopoietic cells of erythroid lineage.